Only those that don’t read thoroughly, can’t code properly, is having networking issues, possibly power issues… oh and even the “experts” will get that occasionally as well 
So basically everyone 
Yes, it is a common error saying something is preventing proper connection between your MCU and the server.
And since you can run it the first time, then it sounds like you have flooded or timed out the heartbeat.
But without more details and posting your properly formatted code (see Welcome Topic - and we don’t want to use your links) as well as doing some reading of the Documentation and Help Center (Links all at the top of this page) and of course, searching this forum for this common issue and answers (are you running everything in the void loop() or using timers - correct answer is NO and YES )
Post your formatted code here and we will see what we can do to assist.